Known hand held bar code readers are of two types. The first is a "pen" type or contacting wand which outputs a focused light beam and detects a return beam at the pen tip. The pen must be manually scanned across the bar code. The second is a "gun" type self scanning bar code reader which uses a focused laser beam moved across a target bar code by a rotating mirror. Examples of self scanning bar code readers are disclosed in U.S. Pat. Nos. 4,409,470, 4,736,095, 4,758,717, 4,808,804, 4,816,661 and 4,845,350 assigned to Symbol Technologies Inc. of Bohemia, N.Y.
The motors used by rotating mirror scanners have a short lifetime and their reading speeds are limited because of mirror motion to less than a hundred readings per second. An alternative self scanning technique for reading bar codes that eliminates the need for the mechanical scanning by imaging the bar code onto a linear CCD detector array. The elements in the CCD array are then electronically scanned to yield a signal that is proportional to the reflected light intensity of the bar code.
This technique eliminates the need for mechanical scanning and offers higher reading speeds in excess of ten times those of mechanical scanners. A major drawback with non-moving self-scanners' problem is that, the F number of the detector optics must be chosen to enable sufficient light to be presented to the CCD array, yielding a correspondingly small depth of field. This limits the usefulness of those type of devices to reading only bar codes at fixed distances.